The extreme weather, eerily similar to the disastrous 2003 fires just over a week from the disaster's 10th anniversary, combined searing heat, severe winds, and low humidity for much of Tuesday.

A series of about 13 grass fires, including one deliberately lit by teenagers, were quickly pounced on by firefighters, the largest reaching just 500m by 100m before being extinguished.

No homes or properties were threatened in Canberra, and the three fires lingering on the territory's outskirts in Namadgi National Park did not flare up. The worst effects of the catastrophic fire conditions that engulfed the region were seen in the ACT's immediate surrounds.

A fast moving grass fire destroyed at least one home near Jugiong, to the ACT's west, while a further 20 homes were still under threat late on Tuesday night. That fire also reportedly cause major stock loss. Fire was also threatening 30 homes at the Kybeyan Valley, near Cooma.

About 40 homes were under threat as fires tore through 1000ha of grasslands and dense acacia scrubland off the Kings Highway, east of Bungendore, late on Tuesday night. On Hazeldell Road, Rural Fire Service crews raced from property to property warning residents of the impending danger.

The Kings Highway had to be closed and local RFS crews said at least one home was ''impacted'' from fires.

Fires raged out of control in many parts of southern NSW, around Crookwell, Bega, Nowra, and around Tarcutta and Wagga Wagga. More than 140 fires raged across NSW, burning through over 65,000 hectares. Thirty of those fires were still uncontained by 8.30pm.

The strong winds, gusting up to 90km/h, caused havoc across Canberra, bringing down branches and trees across roads, cars, and properties, prompting 149 calls for help.

High winds also caused temporary blackouts across the city, and the searing temperatures, reaching a maximum of 38 degrees at 4.08pm, left 15 people in hospital with heat-related illness.

Rural Fire Service Chief Officer Andrew Stark said the conditions were the worst seen in the ACT in years.

Mr Stark praised the efforts of his firefighters, who were able to contain the Canberra fires before they spiraled out of control.

''We're not quite through it yet, but this is certainly the best we could have hoped for,'' Mr Stark said.

''This is our first taste, we've been very fortunate, we'll just continue to work on what we're doing, it'll be a busy couple of days,'' he said.

The fire danger is expected to fall from extreme to a very high danger in the ACT as temperatures and winds ease on Wednesday. A total fire ban will remain in place, largely due to the fires burning in neighbouring NSW.

But the ACT will enjoy only a brief respite from the dangerous fire conditions.

Mr Stark warned Saturday's

forecast was for an ''almost carbon copy of today's conditions'' with high temperatures, strong winds and a late southerly change, which he said would be ''challenging''.

A dust cloud moved in over the ACT yesterday, and dry lightning was seen late in the afternoon.

The grass fires burning in suburbs including Fyshwick, Macquarie, Higgins, Kambah, Gungahlin, Bonython, Greenway, Belconnen and at Oaks Estate in Queanbeyan were mostly sparked by clashing power lines.

Mr Stark said each of those fires had the potential to threaten lives and property were it not for quick action by residents and fire crews.

''There's been a number of fires and they've all been lapped up very quickly because they were reported quickly by the community through Triple-0,'' he said.

Two minors, aged 13 and 14, were caught by police after deliberately lighting a fire on Baldwin Drive in Lawson. Both have been released to their parents and will undergo restorative justice.

The ACT will send aid to NSW firefighters as they continue to battle multiple fires in the region.

A strike team of five vehicles and a commander will be sent to the southern ranges, while relief will be sent to Queanbeyan Fire Station.

ACT Fire and Rescue have also sent an urban fire pumper, a water tanker and a commander to Cooma.

Emergency Services Minister Simon Corbell, who spent much of the day at the ESA's Fairbairn headquarters, said the directorate was now preparing for a repeat of Tuesday's conditions this weekend.

''Saturday is expected to be very severe conditions again,'' Mr Corbell said.

The total fire ban will mean nature reserves and some roads will remain closed on Wednesday.